1. Field of the Invention
This invention relates to apparatus and methods for collection and analysis of gases respired by a patient and further for capnometric analysis of those gases for content of carbon dioxide and other gases.
2. Description of the Prior Art
During anesthesia, and especially during sedation anesthesia or analgesic anesthesia, it is often desirable to collect and analyze qualitatively and quantitatively the constituents of gases respired by the patient. During such procedures, it is further desirable to avoid or minimize the use of gas delivery and collection apparatus that is so large or complicated that it interferes with anesthesia procedures or surgical procedures or interferes with a clear, unobstructed view of the patient's face and respiration passages. Furthermore, it is desirable during such procedures to avoid or minimize contact between the gas delivery and collection apparatus and the patient's mouth and other facial areas, especially to assure optimum comfort of the patient and freedom from claustrophobic reaction in the patient. The prior art discloses several types of apparatus and methods intended to alleviate those problems and achieve those objectives.
U.S. Pat. No. 4,248,218 to Fischer discloses a scavenging mask apparatus for administering gas to a patient and scavenging the gas while preventing its leaking to the ambient atmosphere. That patent describes use of nasal cannulas for delivery of gas and emphasizes maintaining a substantially fluid tight seal between the mask and surfaces of the patient's face. There is no disclosure in that patent of means for simultaneous or alternate, separate, selective collection and analysis of exhaled or inhaled nasal gases and exhaled or inhaled oral gases.
U.S. Pat. No. 4,265,239 to Fischer, Jr., et al. discloses another type of apparatus to limit or prevent escape of anesthetic gases into the ambient atomosphere of a dental orperatory. Leaking gases are drawn by vacuum into a gas exhaust chamber formed between adjacent, separated mask walls. That patent teaches maintenance of fluid tight contact between the edges of the mask and the facial surfaces of the patient and does not describe any method for selective, simultaneous or alternate, separate, selective, collection and analysis of gases respired via the patient's nose and mouth.
U.S. Pat. No. 4,763,664 to Merilainen discloses apparatus for collecting exhaled gases to determine carbon dioxide content and respiratory quotient, which apparatus consists of a closed, transparent canopy or container surrounding the patient's head and sealed around the patient's neck. That patent does not describe any apparatus or method for selective, separate or combined, simultaneous collection of orally and/or nasally respired gases.
U.S. Pat. No. 4,807,617 to Nesti discloses a double mask type apparatus with a fluid tight seal between the delivery mask and the facial surfaces of the patient and an evacuated exhaust chamber between the delivery mask and the exhaust mask to capture gases leaking around the edges of the delivery mask. That apparatus can be used only with standard, prior art delivery mask apparatus. That patent contains no description of an apparatus or method for selective, separate or simultaneous collection and analysis of orally and/or nasally respired gases.
A number of prior art patents disclose apparatus for delivery of inhalation gases to the atmosphere near the patient's nose and mouth while maintaining the gas delivery apparatus out of contact with the patient's facial surfaces. For example, U.S. Pat. No. 3,877,691 to Foster discloses a pair of concave shield panels which are joined around their peripheral edges to form between them an exhaust chamber for gases exhaled by the patient which flow into the shield apparatus through apertures in the arcuate panel proximal to the patient's face. Attached to the interior surface of the perforated arcuate panel is a delivery tube for oxygen. U.S. Pat. No. 3,403,677 to Struve discloses a facial surgical drape support including a perforated tubular loop for introduction of oxygen or air into the space between the supported drape and the patient's face. U.S. Pat. No. 4,739,753 to Brehm discloses a surgical drape support including a delta-shaped gas supply nozzle, spaced above the patient's face and having apertures directing to the patient's breathing area a supply of air, oxygen or anesthetic gases. U.S. Pat. No. 3,530,515 to Jacoby describes a surgical drape support including a rigid frame member supporting a flexible oxygen tube which is spaced from, and directed toward, the patient's breathing passages. U.S. Pat. No. 2,628,803 to Krewson discloses a surgical drape support which has mounted above the patient's face a rigid, slotted plate or cup to be used in administering anesthetics to the patient. None of those patents describes any method or apparatus for the selective, separate simultaneous or alternate collection and discriminating analysis of orally and/or nasally respired gases.
Other prior art patents disclose additional types of apparatus adapted to collect and/or analyze exhaled gases. For example, U.S. Pat. No. 4,848,366 to Aita, et al, describes a mask covering the users nose, mouth, chin and cheeks and forming a substantially fluid tight chamber around those facial areas for containing exhaled gases which are exhausted from that chamber by a self-contained exhaust fan system carried on the user's body. That patent does not describe any method or apparatus for selective, discriminating collection and removal, separately or simultanously, of respired nasal gases and respired oral gases.
U.S. Pat. No. 3,395,701 to Bartlett, et al, discloses apparatus for collecting, isolating and analyzing expired gases to measure the oxygen content therein. That apparatus can be used only with standard, prior art oxygen breathing masks and makes no provision for selective, separate or simultaneous discriminating collection and analysis of respired nasal and oral gases.
Apparatus manufactured by Nellcor Incorporated of Hayward, California for delivery of inhalant oxygen gas and collection of expired carbon dioxide includes an apparatus body mounted under the patient's nose and a pair of separate cannulas, each extending into a separate nare of the patient. One cannula delivers oxygen to the patient and the other cannula collects exhaled carbon dioxide. That apparatus does not provide for the selective, separate, simultaneous or alternative collection and discriminating analysis of respired oral and/or nasal gases.
There remains a need for a method, and for simply constructed, light weight apparatus, for selective, discriminating separate and/or simultaneous collection and analysis of respired nasal and/or oral respired gases which can be used while avoiding substantial contact with the facial surfaces of the patient.